Dynamic Test Conditions Research Articles

Kinetic models for the SR1500 and LY556 epoxies under manufacturer’s recommended cure cycles

The kinetic behaviours of two commercial epoxy resin systems subjected to manufacturer’s recommended cure cycles (MRCC) were studied in detail. The two systems were characterized through differential scanning calorimetry (DSC) using both isothermal and dynamic test conditions. The kinetic parameters were determined and two original kinetic models were established for these resin systems subjected to the “real” processing conditions. In this paper the experimental procedure is described, together with its results and the original kinetic models developed.

Computerized dynamic posturography analysis of balance in individuals with a shoulder stabilization sling.

Sling immobilization of the upper limb may affect balance. Computerized dynamic posturography (CDP) provides a validated, objective assessment of balance control and postural stability under dynamic test conditions. We tested the balance of individuals with a shoulder stabilization sling (SSS) using an EquiTest machine to objectively assess imbalance while wearing a sling. Forty-two right hand dominant (RHD) adults (16 females, 26 males; average age 22 years; range 20-35years) were included in the study, comprising six controls and two SSS groups with 18 dominant hands (DH) and 18 non dominant hands (NDH). CDP assessed balance by the Sensory Organization Test (SOT), Motor Control Test (MCT), and Adaptation Test (ADT). The composite equilibrium scores (CES) were as follows: controls 80.8%, sling DH 71.1 versus sling NDH 69.6%. Sling use has lower CES compared to controls (p=0.025). The use of a sling caused 31% of subjects to have decreased CES. 22.9% of sling users had imbalances. Among sling users, the DH group had 19.1% imbalances compared to 26.8% for the NDH group (p=0.044). There were six absolute falls in the DH group versus 12 in the NDH group. Wearing a sling causes balance decompensation in almost one-third of healthy volunteers, and this is greater when worn in the non dominant hand, with double the number of falls. This has significant implications for patients having prolonged use of a sling. Consideration should be given to operative procedures or conservative management of shoulder pathology where sling use is required and promotion of the early discontinuation of sling use can be considered.

Experimental and modeling study of dynamic mechanical properties of cement paste, mortar and concrete

Understanding the strain rate effects on cement-based materials are important for accurately modeling concrete structure damage to high-velocity impact and blast loads. This paper reports experimental results of the strain rate effect on paste, mortar and concrete. A pulse-shaped split Hopkinson pressure bar (SHPB) was employed to determine the dynamic compressive mechanical responses and failure behavior of paste, mortar and concrete under valid dynamic testing conditions. Quasi-static experiments were conducted to study material strain rate sensitivity. Strain rate sensitivity of the materials is measured in terms of the stress–strain curve, elastic modulus, compressive strength and critical strain at peak stress. Empirical relations of dynamic increase factor (DIF) for the material properties are derived and presented. A compressive constitutive model with strain rate and damage effects was modified to accurately describe the dynamic compressive stress–strain curves of the materials.

Experimental Investigation of Rheological and Morphological Properties of Water in Crude Oil Emulsions Stabilized by a Lipophilic Surfactant

Rheological behavior of two crude oils and their surfactant-stabilized emulsions with initial droplet sizes ranging from 0.5 to 75 µm were investigated at various temperatures under steady and dynamic shear testing conditions. In order to evaluate the morphology and Stability of emulsions, microscopic analysis was carried out over three months and average diameter and size distribution of dispersed droplets were determined. The water content and surfactant concentration ranged from 10 to 60% vol/vol and 0.1 to 10% wt/vol, respectively. The results indicated that the rheological properties and the physical structure and stability of emulsions were significantly influenced by the water content and surfactant concentration. The crude oils behaved as Newtonian fluids over a wide range of shear rates, whereas the emulsions behaved as non-Newtonian fluids, indicating shear-thinning effects over the entire range of shear rates. The viscosity, storage modulus and degree of elasticity were found to be significantly increased with the increase in water content and surfactant concentration. The maximum viscosity was observed at the point close to the phase inversion point where the emulsion system changes from water-in-oil emulsion to oil-in-water emulsion. The results also indicated that the rheological properties of crude oils and their emulsions are significantly temperature-dependent.

Decision Making in Surgical Treatment of Chronic Low Back Pain: The performance of prognostic tests to select patients for lumbar spinal fusion

Decision Making in Surgical Treatment of Chronic Low Back Pain: The performance of prognostic tests to select patients for lumbar spinal fusion

Biomechanical comparison of an angular stable plate with augmented and non-augmented screws in a newly developed shoulder test bench

BackgroundThe proximal humeral fracture is one of the most common fractures. Although there are a number of treatment options available, the clinical outcomes in geriatric patients are still unsatisfactory. Therefore, the aim of this study was to investigate the biomechanical behaviour of an angular stable plate with either augmented or non-augmented screws using two different fracture models in a shoulder test bench with active muscle forces. MethodsSix paired fresh-frozen humeri were loaded into a shoulder test bench simulating ab- and adduction between 15 and 45° induced by active muscle forces. The bone mineral density was measured by a quantitative CT. A two-part fracture model (stable and an unstable) was used to investigate the different biomechanical behaviours of the PHILOS plate, either utilising cannulated screws, allowing in situ augmentation, or without utilising augmented screws. Four screws were augmented with 0.5ml PMMA cement. FindingsThe in vitro-measured resulting forces in the glenoid fossa were comparable to the in vivo forces generated in shoulder arthroplasties. Under stable conditions, the per cycle motion and varus impaction tilting showed no significant difference. In the unstable state, the augmented group showed a maximum of 0.81° per cycle motion and a maximum varus impaction of −1.46° compared to the non-augmented maximum of 2.31° per cycle motion and maximum varus impaction of −4.26° (P<0.05). InterpretationIn an unstable fracture model under dynamic testing conditions, augmentation leads to a decreased per cycle motion and varus impaction of the humeral head.

Design and measurement of a piezoresistive triaxial accelerometer based on MEMS technology

With the springing up of the MEMS industry, research on accelerometers is focused on miniaturization, integration, high reliability, and high resolution, and shares extensive application prospects in military and civil fields. Comparing with the traditional single cantilever beam structure or “cantilever-mass" structure, the proposed structure of “8-beams/mass" with its varistor completely symmetric distribution in micro-silicon piezoresistive triaxial accelerometer in this paper has a higher axial sensitivity and smaller cross-axis sensitivity. Adopting ANSYS, the process of structural analysis and the manufacturing flow of sensing unit are showed. In dynamic testing conditions, it can be concluded that the axial sensitivity of x, y, and z are Sx = 48 μV/g, Sy = 54 μV/g and Sz = 217 μV/g respectively, and the nonlinearities are 0.4%, 0.6% and 0.4%.

Evaluation of Scale Inhibitors in Marcellus High-Iron Waters

Summary The Marcellus waters of Pennsylvania and West Virginia commonly contain elevated levels of calcium, barium, and iron. Theoretical analyses of these waters indicate a propensity toward the formation of calcium carbonate, barium sulfate, strontium sulfate, and iron-related scales. The high level of dissolved iron commonly present in the water adversely affects the ability of the scale inhibitor to inhibit calcium carbonate scale. In this study, the inhibition performance of two new chemicals and some commercial products was evaluated under static and dynamic test conditions using synthetic Marcellus waters at varying iron concentrations. It was shown that both new chemicals were able to control calcium carbonate scale effectively in the presence of dissolved iron up to 200 ppm, whereas the performance of polycarboxylic acid, amino tri(methylene phosphonic) acid, and carboxymethyl inulin dropped sharply even in the presence of small amounts of Fe2+ (5 ppm). The inclusion of iron-sequestering agents with these chemicals and the effect of iron upon calcium sulfate inhibition are also discussed in this paper.

Design, construction, and evaluation of a dynamic MR compatible cardiac left ventricle model

Development of magnetic resonance (MR) sequences is important to answer clinical questions and to overcome current limitations. To meet the challenges of cardiac MR, dynamic and reproducible testing conditions are required. We aimed at developing a dynamic MR-compatible cardiac left ventricle model that imitates myocardial tissue properties and simulates dynamic motion. A dynamic left ventricle silicone model was designed to match myocardial T(1) and T(2) relaxation times. Silicone mixtures were explored to replicate T(2) values of myocardial edema. A controllable piston pump was constructed to produce pulsatile flow paradigms. They were validated against flow sensors and MR data, including SSFP-based and phase-contrast-based sequences. A dedicated software interface was developed for the control. Model dimensions represented cardiac left ventricle dimensions of healthy men. The range of end diastolic volumes was 85-175 ml, depending on the driven stroke volume. Stroke volume quantification for flow paradigms of 30∕60∕90∕120 ml resulted in 29.2∕57.6∕88.8∕118.4 ml by MR volumetry, 29.6∕59.9∕89.4∕119.0 ml by phase contrast measurements, and 29.9∕60.4∕91.1∕120.9 ml by flow meter revealing consistency. The system accurately replicated physiological and pathophysiological flow paradigms. The silicon model exhibited T(1) of 1002 ± 8 ms, T(2) of 58 ± 1 ms. Signal intensities (a.u.) of the ventricle model were 128 ± 23 for FGRE (vs 138 ± 17 in vivo) and 1156 ± 37 for b-SSFP (vs 991 ± 96 in vivo). T(2) of 75 ± 2 ms was achieved for the myocardial pathology. We developed a controllable left ventricle model resembling MR signal characteristics of human myocardium, including pathological conditions, and allowing for the replication of contraction and flow paradigms.

Hemocompatibility of Inorganic Physical Vapor Deposition (PVD) Coatings on Thermoplastic Polyurethane Polymers.

Biocompatibility improvements for blood contacting materials are of increasing interest for implanted devices and interventional tools. The current study focuses on inorganic (titanium, titanium nitride, titanium oxide) as well as diamond-like carbon (DLC) coating materials on polymer surfaces (thermoplastic polyurethane), deposited by magnetron sputtering und pulsed laser deposition at room temperature. DLC was used pure (a-C:H) as well as doped with silicon, titanium, and nitrogen + titanium (a-C:H:Si, a-C:H:Ti, a-C:H:N:Ti). In-vitro testing of the hemocompatibility requires mandatory dynamic test conditions to simulate in-vivo conditions, e.g., realized by a cone-and-plate analyzer. In such tests, titanium- and nitrogen-doped DLC and titanium nitride were found to be optimally anti-thrombotic and better than state-of-the-art polyurethane polymers. This is mainly due to the low tendency to platelet microparticle formation, a high content of remaining platelets in the whole blood after testing and low concentration of platelet activation and aggregation markers. Comparing this result to shear-flow induced cell motility tests with e.g., Dictostelium discoideum cell model organism reveals similar tendencies for the investigated materials.

An improved dynamic test method for solar collectors

A comprehensive improvement of the mathematical model for the so called transfer function method is presented in this study. This improved transfer function method can estimate the traditional solar collector parameters such as zero loss coefficient and heat loss coefficient. Two new collector parameters t and mfCf are obtained. t is a time scale parameter which can indicate the heat transfer ability of the solar collector. mfCf can be used to calculate the fluid volume content in the solar collector or to validate the regression process by comparing it to the physical fluid volume content if known. Experiments were carried out under dynamic test conditions and then test data were processed using multi-linear regression method to get collector parameters with statistic analysis. A comparison of the collector parameters obtained from the improved transfer function (ITF) method and the quasi-dynamic test (QDT) method is carried out. The results show that the improved transfer function method can accurately obtain reasonable collector parameters. The influence of different averaging time intervals is investigated. Based on the investigation it is recommended to use on line calculation if applicable for the second-order differential term with 6–9min as the best averaging time interval. The measured and predicted collector power output of the solar collector are compared during a test of 13days continuously both for the ITF method and the QDT method. The maximum and averaging error is 53.87W/m2 and 5.22W/m2 respectively of the ITF method while 64.13W/m2 and 6.22W/m2 of the QDT method. Scatter and relative error distribution of the measured power output versus the predicted power output is also plotted for the two methods. No matter in either error analysis or scatter distribution, the ITF method is more accurate than the QDT method in predicting the power output of a solar collector.In conclusion, all the results show that the improved transfer function method can accurately and robustly estimate solar collector parameters and predict solar collector thermal performance under dynamic test conditions.

Dynamic tests of cemented paste backfill: effects of strain rate, curing time, and cement content on compressive strength

This article investigates the compressive strength of cemented paste backfill (CPB) under dynamic loading. To accommodate the low impedance CPB, a modified split Hopkinson pressure bar (SHPB) system is adopted. In contrast to traditional solid steel transmitted bar, a hollow aluminum transmitted bar is introduced to reduce the impedance. With this system, the dynamic stress equilibrium is achieved, which guarantees the valid dynamic material testing condition. The dynamic tests are conducted for CPB with different cement contents and curing time. It is observed that: (1) for CPB with the same curing time and cement content, the dynamic strength increases with the strain rate, (2) for CPB with the same cement content, the dynamic strength increases with the curing time, and (3) for CPB with the same curing time and tested under similar strain rate, the dynamic strength increases with the percentage of cement. This observation can be understood by considering the hydration process of cements.

The progression from obesity to type 2 diabetes in Alström syndrome

Alström syndrome (ALMS) is a rare autosomal recessive monogenic disease associated with obesity, hyperinsulinemia, and alterations of glucose metabolism that often lead to the development of type 2 diabetes at a young age. To study the relationship between weight and metabolism in a group of ALMS patients and matched controls. Fifteen ALMS patients (eight males, seven females; aged 3-51) were compared in a cross-sectional study with an age- and weight-matched control population. Anthropometric parameters, fat mass, glucose and insulin secretion in basal and dynamic oral glucose tolerance test (OGTT) conditions were measured. Furthermore, anthropometric and body composition data were obtained from an international group of 27 ALMS patients (13 males, 14 females, age range: 4-29 yr). In ALMS we observed an inverse correlation between age and standard deviation scores for height, weight, and body mass index. The OGTT glycemic curves of ALMS subjects were similar to those of age-matched controls, whereas insulin response was clearly greater. In ALMS individuals the insulin response showed a reduction with age. We documented pathologic values of the derived indices homeostasis model assessment of insulin resistance (HOMA-IR), insulin sensitivity index, HOMA%β-cell and insulinogenic index in ALMS, but unlike the insulin-resistance indices, the β-cell function indices showed a significant reduction with age. In ALMS the progression from the early onset obesity toward the impaired fasting glucose or impaired glucose tolerance and overt diabetes is mostly because of a progressive failure of β-cell insulin secretion without any further worsening of insulin resistance with age, even in the presence of weight reduction.

Dynamic Testing, Working Memory, and Reading Comprehension Growth in Children With Reading Disabilities

This longitudinal study assessed (a) whether performance changes in working memory (WM) as a function of dynamic testing were related to growth in reading comprehension and (b) whether WM performance among subgroups of children with reading disabilities (RD; children with RD only, children with both reading and arithmetic deficits, and low verbal IQ readers) varied as a function of dynamic testing. A battery of memory and reading measures was administered to 78 children (11.6 years) across three testing waves spaced 1 year apart. WM tasks were presented under initial and dynamic testing conditions (referred to as gain and maintenance testing). The important results were that (a) WM performance as a function of maintenance testing was a significant moderator of growth in reading comprehension and (b) WM performance of children with RD was statistically comparable within subgroups of RD but inferior to that of skilled readers across all testing conditions. The results support the notion that children’s WM performance under dynamic testing conditions was related to the rate of growth in reading comprehension but unrelated to subgroup differences in reading.

Normative Data for the Subjective Visual Vertical Test during Centrifugation

The otoliths act as gravito-inertial force sensors and contribute to the perception of spatial orientation. The perception of gravitational vertical can be assessed by asking a subject to adjust a light bar to the vertical. Prior to clinical use of the SVV (subjective visual vertical) test, normative data and test-retest reliability must be established. To obtain normative data and d etermine the test-retest reliability for the SVV test performed in static and dynamic test conditions. A descriptive design was used to obtain normative data. Twenty-four young adults with no history of neurological disease, middle-ear pathology, open or closed head injury, cervical injury, or audiovestibular disorder participated in the study. The SVV angle was measured in the static position and in three dynamic conditions: (1) on-axis clockwise (CW) rotation, (2) off-axis CW rotation of right ear, and (3) off-axis CW rotation of left ear. In young healthy individuals, the SVV was <2° for static and on-axis rotation, and shifted up to 11° during unilateral centrifugation. Test-retest reliability of the SVV was good for all test conditions. The normative data obtained in this study may be useful in identifying patients with chronic utricular dysfunction. We recommend the use of difference angles (on-axis SVV - off-axis SVV) to remove baseline bias and decrease the variability of the SVV angles for the off-axis conditions.

Amine treatment of hydrogen sulfide-containing gases using carbon nanomaterials

The prospects for improving the method of adsorption purification in using carbon nanomaterials combined with activated carbons or macroporous adsorption materials as the adsorbent was demonstrated. The results of experimental studies of the adsorption properties of a nanocarbon material – filamentary carbon – in model solutions of ethanolamine containing SF are reported. It was found that in static and dynamic testing conditions, the new material has higher adsorption indexes among activated carbons, including in comparison to the AG-3 and AG-2 carbons widely used in industrial sulfur scrubbers.

Stab Resistance of Thermoset-Impregnated UHMWPE Fabrics

The stab resistance of thermoset(TS) impregnated, woven UHMWPE fabric with additional steel fabrics was investigated under dynamic stab testing conditions. Vinyl-ester resin was coated on the UHMWPE fabrics with hand lay-up process to fabricate the composite and the mental fabrics were laminated on the composites. Dynamic stab testing of targets was based on GA68-2008 for stab resistance of body armor. Six uniform specified knives impactor were used for testing. And the samples are found to present significant improvements in stab resistance (knife threat) over neat fabric targets of equal areal density. Photographs show that resin primarily reduces the mobility of yarns and enables them to stop the knife penetration more effectively in the damage zone. These results indicate that the penetration of knives through such multilayer fabrics is effectively prevented and the process could be used to fabricate flexible body armors that provide improved protection against stab threat.

Does the Dynamic Testing of Working Memory Predict Growth in Nonword Fluency and Vocabulary in Children With Reading Disabilities?

This three-year longitudinal study assessed whether working memory (WM performance) when tested under dynamic testing conditions is related to growth on measures of phonological awareness and vocabulary in skilled readers and subgroups of children with reading disabilities (RD) (children with RD-only, children with both reading and arithmetic deficits, and low verbal IQ readers). A battery of memory and reading measures was administered to 78 children (11.6 yrs) across three testing waves spaced one year apart. WM tasks were presented under initial, gain, and maintenance testing conditions. The important results were (1) growth curve modeling showed that WM performance administered under initial and maintenance testing conditions was a significant moderator of growth in receptive vocabulary, whereas the number of probes and WM performance under gain testing conditions were significant moderators of growth in nonword fluency and (2) WM performance was statistically comparable within subgroups of children with RD, but inferior to skilled readers across all testing conditions. The results support the notion that children’s WM performance when measured under dynamic testing conditions was related to the rate of growth on basic reading and vocabulary measures.

Full-field Strain Analysis of a Ski Boot

The quality of the ski boots plays an extraordinary important role in the performance and in the safety of the skiers. The deformation behavior of a racing class ski boot was characterized by using the digital image correlation technique in this study. The boot was gripped in the ski binding and 3 types of motions of the skiers and the deformations of the boot were simulated by a professional skier in the laboratory. First, the buckles were closed in 4 stages and the resulting strains were measured. Furthermore, the skier positioned his balance continuously forward, resulting in a high overall bending deformation of the boot. The leg of the skier acted as a bending arm and pushed the upper part of the boot forward. This loading situation was assumed as quasi- static and was repeated several times. Finally, the skier jumped and this dynamic movement was recorded by using two high speed cameras for 3D analysis. Special focus was devoted to the measurement of the deformation of the boot during the contact of the ski with the ground of the laboratory. Both the displacement of the upper part and the local strain in selected areas of the boot was determined for both quasi-static and dynamic test conditions and are discussed in the paper.

VOC Outgassing from Baked and Unbaked Ventilation Filters

Volatile organic compounds (VOC) outgassing from newly manufactured baked and unbaked ventilation filters were examined using gas chromatography/mass spectrometry following thermodesorption (TD-GC/MS) technique. Filters were tested under both static and dynamic conditions. Under static conditions, the unbaked filter outgassed VOC (0.50 ± 0.18 μg) more than twice as much as the baked filter (0.23 ± 0.15 μg). 2-Propanol and nonanal were the components outgassed from both baked and unbaked filters and 4-piperidinol, 2,2,6,6-tetramethyl- was determined to be the main contaminant outgassed from the unbaked filters. Series of tunnel experiments were conducted by passing highly purified dry air through the filters and taking air samples upstream and downstream the filter. Under dynamic test conditions, the baked filter was not significantly distinguishable from the background with a downstream total VOC concentration increase only by 35.3%, which was almost 9 times lower than that of the unbaked filter (294%). 3-hydroxy-4,6-di-t-butyl-2H-pyran-2-one was the main VOC outgassed from the unbaked filter. In addition, a general trend of decreasing VOC outgassing with time from baked and unbaked filters was observed in both static and dynamic tests. It also suggested that baked filter behaved like a sink for certain VOC and unbaked filters from different batches may outgas different VOC. Overall, bake-out was proved to be an effective way of reducing VOC outgassing from ventilation filters.